A chain saw including an endless chain (saw chain) has been used for cutting down or pruning trees, bamboos, or the like. The endless chain is rotated by a lever when such a chain saw is used.
Such a chain saw incorporates a braking system. When, e.g., the chain saw is accidentally dropped onto the ground or beaten strongly against a tree and, thereby, an impact is applied thereto, the braking system is activated to stop the drive of the chain to prevent the chain from being damaged. The braking system includes, e.g., a drum coupled to the rotary shaft of a sprocket with which the chain is engaged, a belt wound around the drum, and a spring disposed on one end of the belt. The belt is pulled by a biasing force of the spring to tighten the rotating drum to thereby stop the rotation thereof.
Such a chain saw has a driving source such as an engine or electric motor and a centrifugal clutch interposed between the driving source and chain. When an operating lever is operated to make the driving source rotate at high speed, the centrifugal clutch is brought into an engagement state, whereby a driving force is transmitted to the chain. On the other hand, when the operating lever is returned to its initial position to decrease the rotation speed of the driving source, the centrifugal clutch is brought into a disengagement state.
However, in the above arrangement, even when the operating lever is returned to its initial position to bring the centrifugal clutch into a disengagement state, the chain is not stopped immediately by virtue of rotational inertia. In order to cope with such a disadvantage, there is proposed an electric-motor driven chain saw having a mechanism that pulls the other end (opposite side to the side on which the spring is disposed) of the belt wound around the drum of the abovementioned braking system (see, e.g., Patent Document 1).
Patent Document 1: Japanese Patent No. 3263284 (columns [0024] to [0027], FIG. 3)